Valve control for vibrator and like apparatus operating on elastic fluid



y 1966 A. H. PETERSON 3,253,514

VALVE CONTROL FOR VIBRATOR AND LIKE APPARATUS OPERATING 0N ELASTIC FLUIDFiled Feb. 6, 1964 FIG. 2

FIG. 3

INVENTOR. AXEL H. PETERSON ATTORNEY United States Patent 9 3 253 514VALVE conrnor. rota vianAron AND LIKE Al- PARATUS OPERATING on ELAsrrcFLUID Axel H. Peterson, 4431 th Ave., Rock Island, lll. Filed Feb. 6,1964, Ser. No. 342,937 16 Claims. c1. 91 s0 This invention relates to aforce-applying apparatus and more particularly to that type of apparatusin which the force is derived from elastic fluid such as compressed airand is converted to mechanical forces for use in mechanisms employed forvibrating, shaking, pounding, punching, impacting etc. Moreparticularly, the invention relates to improvements in devices forregulating the admission of elastic fluid pressure in -explosive burstsas distinguished from virtually non-compressible fluids such as oil,etc.

Exemplary of this general type of apparatus is that forming the subjectmatter of co-pending application Serial No. 318,638, filed October 24,1963, in which a hammer or weight is carried in a cage or equivalentsupport for reciprocation toward and away from, for example, a platewhich may be attached to an object to be vibrated, such as aload-carrying container in which the vibratory forces imparted to thecontainer facilitate unloading. In the absence of the striker plate, thecage or hammer support may be attached directly to such container orother object, or the hammer or weight may be used for punching, piledriving etc. In still other instances, the hammer need not strike thestriker plate or its equivalent but the reciprocatory motion developedmay be utilized without the impact. In the example referred to, thehammer cage is divided or separated from an inlet chamber by a partitionhaving an opening therein with which a valve cooperates for theintermittent admission of air to piston means associated with the hammerand operating in an expansive or power chamber. Each time air orequivalent fluid pressure is introduced to the piston means, the hammermoves away from the partition on what may be regarded as a power stroke.Depending upon the position and location of the apparatus, the hammerhas a return stroke on which it is biased, either by its own weight orby other biasing means. The arrangement in the application referred tois such that the control valve and hammer are mechanically independentof each other, and the means for influencing the valve to open and closeincludes passage means, vent means and control of the latter so that asthe hammer moves on its power and return strokes, the valveautomatically opens and closes.

It is a principal object of the present invention to provide an improvedvalve system and control therefor. The improved system featuresconditioning of the valve for reopening by a counter-acting valvechamber and means for trapping and releasing pressure as respects thischamber, the latter phase being dependent on hammer position.Nevertheless, the main valve itself is not engaged by the hammer, as isthe case in still earlier structures. More specifically, it is an objectto time hammer and valve movement so that the full stroke of the hammermay be utilized, which is especially important at relatively higherspeeds. At lower speeds, the hammer normally returnsa full stroke andwaits for the valve to open, in the prior application, but at higherspeeds the valve is apt to open prematurely and thus move the hammerback on its power stroke.

A still further object of the invention resides in a construction inwhich the valvestructure and control therefor may be readilyincorporated in a unit that is easily installed and removed from thebasic supporting structure.

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It is a further object of the invention to exploit these principles in acommercially successful device capable of developing relatively highforces, viz., in the range of twenty to thirty-five foot pounds on aslittle as 40 psi. Such apparatus, using air at as low as one-half tofive cubic feet per minute, may be operated by a fractional horsepowercompressor.

A further object is to incorporate in' such apparatus thecharacteristics of strength, ruggedness and portability; e.g., in weightranges of from 25-100 lbs. so that it may be easily handled by one manas it is moved from job to job.

The foregoing and other important objects and desirable featuresinherent in and encompassed by the invention will become apparent aspreferred embodiments thereof are disclosed in detail in the ensuingdescription and accompanying sheets of drawings, the figures of whichare described below.

FIGURE 1 is a sectional view, with portions in section contained in twoplanes intersecting at the axis of the apparatus, with a source of fluidpressure and associated lines shown schematically.

FIGURE 2 is a fragmentary plan View.

FIGURE 3 is a fragmentary sectional view of a center portion of FIGURE1, showing the valve in its open position.

The vibrator as a whole may be regarded, by way of example, ascomprising a unitary casing structure 10 made up of coaxial parts 12, 14and 16, the latter being a cover rigidly but removablyjoined to the part14 by a circle of cap screws 18. In the illustrated use-environment, theunit is mounted on a typical object to be vibrated (represented at 20)and hence part 12 is lowermost; but, as will be clear from what ensuesherein, this position does not exclude others. The unit may be removablyattached to such object by providing the part 12 as an attaching flangehaving bolt-receiving openings 22. Parts 12 and 14 are joined togetherby a circle of bolts 24 including cushion springs 26.

Part 14, which may be a casting, forms a hammer cage or support 28within which a hammer or its equivalent mass 39 is reciprocable onalternate strokes (here vertical) between upper and lower limits suchas, respectively, the top surface 32 of part 12 and the under surface ofa partition 34 between upper and lower portions of the part 14. Thatportion of cage 28 between hammer 30 and partition 34 establishes apower cylinder or expansive chamber 36, shown expanded in FIG. 1 becausethe hammer is down but capable of contraction as the hammer moves up(FIG. 3). The top end of the hammer is thus a movable wall or pistonmeans 38 acting on or in conjunction with the ham-mer. The top end ofchamber 36 is vented at 40 to enable discharge thereof on the up orreturn stroke of the hammer. The bottom end of the cage 28. isconstructed to avoid trapping of air below the hamr'ner as the hammer,having a suitable seal 31 with the interior wall or cylinder of thecage, reciprocates during operation. The under surface of part 14 hasradial grooves 15 which are normally closed at their outer ends by anO-ring 17 seated in a matched annular groove 19 and a chamfer 21respectively in parts 12 and 14. This ring can yield to allow trappedair to escape.

As the hammer moves upward from the position of FIG. 1, air isdischarged from the chamber 36 through the vent ill, which is largeenough for this purpose but small enough to avoid wasting air on thepower stroke of p the hammer. If the unit were inverted (as it mightwell be) the hammer would return by gravity. But in its present posture,some other biasing means must be relied on. That selected is a pressuremeans, including a fluid passage 42 controlled by a needle valve 44 andorifice 46 which leads via an L-shaped passage 47 to the bottom of thehammer. For the present, let it be assumed that passage 42 is connectedto a source of elastic fluid under pressure, such as compressed air.Regulation of the needle valve 44 controls the rate of return movementof the hammer, it being understood that the tension in the O-ring 17 issuflicient to prevent leakage from the slots 15 at this time. More willbe said below about the illustrated connection of the passage 42 to apressure source.

The partition 34 separates the power chamber 36 from an upper or inletchamber 48 which is constantly pressurized by an inlet line 50 connectedto a source of elastic fluid (e.g., compressed air) such as acompressor, shown schematically at 54, or to a compressed air line (notshown) such as are available-generally at 100 p.s.i.in most industrialplants, etc. If desired, line 50 may have a conventional pressureregulator valve which allows the air to flow into the chamber 48 at arate determined by the valves capacity, the flow stopping when inletchamber pressure reaches a predetermined pressure (the pre-set maximumof the regulator valve).

Transmission of fiuid pressure from inlet chamber 43 to power chamber36, and control thereof, is achieved by means including the partition 34and a port 56 therein, shown here as circular and centrally located, byway of example. Broadly the geography of the port and its alliedcomponents could be otherwise than as shown.

The central underside of cover 16 has within inlet chamber 48 anintegral depending valve support 58 having a closed upper end 60 and anopen lower end 62, which is the bottom of a valve bore 64 which carriesa main valve 66 equipped with a suitable seal 68. The valve 66 iscoaxial with port 56 and has a lower port-control end 70 and a top end71 exposed to the closed end 60 of the valve bore and forming therewitha valve chamber 84. The valve 66 further has, intermediate thecylindrical port-control portion 70 and the bottom end 62 of support 58,an enlarged annular flange 72. The lesser diameter of portion 78 asrespects the main body of the valve affords a first pressu ereceivablearea 74 (the larger diameter of flange 72 is immaterial, since bothfaces of the flange are exposed to inlet chamber 48). The diameter ofportion 70 and the amount of axial movement of the valve are such thatsaid portion slightly enters the port in the port-closing position ofthe valve (FIG. 1) and is withdrawn from the port in the port-openingposition of the valve (FIG. 3). This portion 70 is supplemented by anannular seal 76, here a conventional O-ring, to perfect closing of theport without expensive lapping of metal surfaces.

Magnetic means, here a circle of separate magnets 78 mounted on theunderside of flange 72 by screws 80, attracts the valve 66 to its closedposition via metallic partition 34. This attractive force is somewhatless than the force on area 74 at predetermined minimum pressureexpressed in pounds per square inch in inlet chamber 48 when valvechamber 84 isat atmosphere. Thus, when the valve is closed (FIG. 1) andheld there by the magnetic means, the effects of chamber pressure onarea 74 will have to exceed the magnetic force, plus other forces to benoted later, in order to open the valve (FIG. 3). This can be termed thepre-set value. In other words, the value the pre-set inlet chamberpressure has in overcoming the magnet hold with a given area at 74.These forces can be readily calculated for devices of different sizes,capacities and rates of operation, and to be taken into account are suchthings as frictional drag of O-ring seal 76, friction between valve 66and valve bore 64 and frictional drag of the seal 68, here also anO-ring, between the valve and the bore, besides strength of magnets,etc. The word rise as used herein is, of course, relative, for the inletchamber pressure can increase relative to valve chamber pressure if thelatter drops. Actually, it is the pressure differential that opens thevalve.

Seal 68 operates as means isolating the valve chamber 84 from inletchamber 48 when valve 66 is closed. In short, when the valve closes port56, both powerchamber 36 and valve chamber 84 are cut off from inletchamber pressure, the rise of which becomes effective,- when themagnetic force is overcome, to open the valve, allowing a rush of airthrough the port and into power chamber 36 to force the piston andhammer downwardly or away from partition 34, which phase of operation isnot retarded by discharge passage 40.

Now, with the hammer down and valve 66 open via inlet chamber pressureacting on pressure area 74, it remains to reclose the valve to cut offair to the power chamber so that the piston-hammer may return as powerchamber air is discharged via vent 40. To accomplish this requires thatsome means be provided to return the valve automatically to closedposition; that is, without, for example, cutting off line 50.

This is achieved, by counteracting at least part of the valve-openingforce by an opposing force so as to effectuate the magnets as anultimate valve-closing means. Briefly, what is done is to providepassage means to lead inlet chamber pressure to valve chamber 84 whereit will act on the second pressure-receiving area provided by top end 71of valve 66, which is opposed to the first area 74. It will beappreciated that when valve 66 is open, the whole lower end thereof isthen acted on by inlet chamber pressure; and in effect the whole upperend 71 is exposed to valve chamber 84.

The passage means here is an axial through passage 88 in valve 66opening at 89 at valve end 70 and made up of a series of counterboresincluding a relatively large bore 90 which opens at 91 to valve chamber84. This passage is normally effective as a charging passage only whenvalve 66 is open, for when the valve is closed (FIG. 1), the lower end89 of the passage opens to the power chamber and, being cut off from theinlet chamber 48, serves then, when properly controlled, as adischarging passage. Also, some means must be provided to absorb themomentum of the opening valve so that it will not destroy itself againstthe bottom end of valve support 58. Such cushion means may also be usedto return the valve to the influence of the closing means comprising themagnets 78.

Typical cushion means may include a coaxial coiled spring 112 looselycarried in valve bore 90 and acting between the valve 66 and the closedend 60 of valve support 58. Although, in the posture of the unit shownhere, gravity would serve to bring the valve 66 back to the reach ofmagnets 78, spring 112 has practical advantages in supplementing themagnetic means, such as overcoming the break away resistance of theO-ring 68, enabling the use of magnets of smaller force, and, as stated,serving as a cushion against extreme valveopening movement.

Control of the passage 88 as respects trapping and releasing fluidpressure in and from chamber 84 is achieved by check valve 114, normallyclosing passage 88 at the shoulder formed by the junction of thatpassage with valve bore 90 and biased to closed position by a relativelylight coil spring 116 disposed loosely within valve spring 112 andacting between the check valve and the closed end of valve housing 58.In addition, means is provided for timing positive opening of the checkvalve with hammer position on the return stroke. A representative meansis shown here as a rod 118 carried by the hammer and having its freeupper end projecting into the open bottom end 89 of passage 88 so as toengage and unseat the check valve 114 in a predetermined position on thehammer return stroke. Obviously, a reversal of parts is available here.

The starting positions of the parts before pressure is applied from line50, can be those shown in FIG. 1. Line pressure when applied via 5450builds up in inlet chamber 48 and before it reaches its pre-set minimum;e.g., 30 p.s.i., while valve 66 is closed, it acts via passage 42-4647,here connected to inlet chamber 48, to move hammer 39 to its upposition, rod 118 opening check valve 114. Valve chamber 84 is thereforeopen to atmosphere via 86-3640. Continued pressure rise in inlet chamber48 acts against pressure area 74 on valve 66 until it overcomes theattractive or holding force of magnets 78 which is, say, eighteen poundsas against a pressure area at 74 of, say, .600 square inch, in whichcase thevalve will quickly open at 30 psi. in the inlet chamber, orapproximately so because of frictional drag and other small variables.The rapidity of valve opening occurs because, as the magnets break awayfrom partition 34, the magnetic attraction deteriorates.

When valve 66 opens, inlet chamber pressure rushes into power chamber36, acting much as an explosive burst on piston 38 to drive hammer 30downwardly. Whether or not the hammer strikes surface 32, a relativelypowerful impulse will result, jarring the object or applying otherdesired force to an equivalent object. As stated above, dischargepassage 40 is so restricted relative to the charge of air bursting intopower chamber 36 as to have no material effect thereon. If desired,adjustment of this passage could be provided as another means besidesneedle valve 44 to vary the rate of return of the hammer. It ispreferred that the hammer should reach or substantially reach its returnlimit (partition 34-) before valve 66 re-opens after closing followingits opening action just described.

Valve 66 closes because of force developed in valve chamber 84 tocounteract the valve opening force, which will be clear by recognizingthat when valve 66 opens it exposes its lower end 70, and thus itspassage 88, to inlet chamber pressure which easily opens check valve 114and enters valve chamber 84 to act against valve area 72, and the checkvalve closes as, ultimately, substantially balancing forces occuragainst both ends of the valve at inlet chamber pressure. The valve isthen conditioned to again come under the attractive influence of themagnets. The expression substantially balancing is used here as one ofconvenience, because exactly equal forces need and may not occur atopposite ends of the valve. For example, the attractive force of themagnets could take effect prior to exact equalization.

Also, when valve 66 opens port 56, there will be a pressure drop in theinlet chamber continuing as the power chamber expands with the pressuretrapped in the valve chamber 84 resulting in a pressure dilferential infavor of valve closing. Factors such as this reveal convenient measuresfor varying the speed of valve closing by varying the rate or time ofequalization, as byjudiciously proportioning the diameter of passage 88.

In this instance, the magnets are assisted by the springs 112 and 116;although, it will be clear that stronger magnets could eliminate thespring 112 (the spring 116 has negligible force in this phase) so far asforces are concerned. Stronger magnets will enable greater valveopening, since their power of attraction is greater and they will havegreater reach for the valve. The spring 112, however, has at least thethree distinct advantages pointed out earlier. If desired, spring 112could be adjusted.

Now, with valve 66 closed, there again occurs the isolation of chambers48, 36 and 84 from one another. Air let into chamber 84 when the valveopens becomes trapped and unless released would prevent re-opening ofthe valve, since area 72 would effectively oppose area 74 and themagnetic vforce could not be overcome. According to the presentinvention, the check valve 114 is positively opened because it isunseated by the rod or element-118 as the hammer reaches the end of itsreturn stroke. This releases the trapped pressure via 89-36-40 andrestores the valve area differential required to escape the magnets orholding means. It will be clear that the length of rod 118 can be variedto change the time of opening of check valve 114. It should be observedthat higher pressures can be introduced into the inlet chamber 48, viathe line 50, than the preset minimum and the intervals can be controlledby dropping the pressure in valve chamber 84 without returning it toatmosphere, for it is the relation of inlet to valve chamber pressurethat allowsthe valve to open and not necessarily the relation toatmosphere. Another significant advantage of the present construction isthat the space between the bottom of the hammer and the top of the part12 is always under pressure, even on the bias .stroke, and, therefore,dust etc. is not inhaled into the bottom ofthe hammer cage.

Features and advantages, other than those categorically enumerated, willreadily occur to those versed in the art, as will many modifications andalterations in the preferred embodiments disclosed, all of which may beachieved Without departure from the spirit and scope of the invention.

What is claimed is:

1. Vibrator apparatus, comprising: means including a pressure-chargeableand discharge-able spower chamber having a hammer and piston meansmovable in one direction upon charging of said chamber and biased forreturn movement upon discharge of said chamber; means including an inletchamber connectible to a source of elastic fluid under pressure; meansincluding a chamber-connecting port, a main valve for opening andclosing the port,

and a valve support movably carrying said valve; valveholding meansreleasably holding the valve closed; means including apressure-chargeable and dischargeable valve chamber operatively relatedto a first pressure area exposed to said valve chamber for acting in aclosing direction on said rnain valve when said valve chamber ischarged; means including a second pressure area acting on the main valveand exposed to inlet chamber pressure and effective upon a predeterminedpressure differential between the valve chamber and inlet chamber infavor of said second area to overcome the holding means for opening saidmain valve; and means for regulating the occurrence of said pressuredifferential including a passage loading at one end to the valve chamberand alternately connoctible at its other end to inlet chamber pressurewhen the main valve is open and to a lower pressure when said main valveis closed so as to respectively charge and discharge said valve chamber,a secondary valve in the passage yieldable to open to inlet chamberpressure when the main valve opens, whereby to charge said valve chamberwith inlet chamber pressure so as to cause reclosing of the main'valve,said secondary valve being arranged to close said passage incident tocharging said valve chamber so as to trap pressure in said valve chamberat a value suflioient to prevent inlet chamber pressure on said secondmain-valve area from immediately re-otpening said main valve, and meansoperative by the hammer and piston means upon predetermined returnmovement thereof to forcibly open said secondary valve to release saidtrapped pressure for discharging the valve chamber and thereby to incursaid predetermined pressure differential in favor of said second area.

2. The invention defined in claim 1, including: casing structurecarrying the power and inlet chambers and having a partition separatingthe chamber, said port being provided in said partition and said valvesupport being disposed in the inlet chamber, said main valve having aport-closing portion exposed via the port to the power chamber, saidpassage having an open end at said portclosing portion of the valveexposed to the power chamber when the main valve is closed and to theinlet chamber when the main valve is open, and the means operative toforcibly open the secondary valve includes an element extending throughsaid open end of the passage means between the secondary valve and thehammer and piston means.

3. The invention defined in claim 2, in which: the passage extendsthrough the valve from said open end to said valve chamber.

4. The invention defined in claim 3, in which: the secondary valve is acheck valve in the passage biased by a closing spring between said checkvalve and the valve support.

5. The invention defined in claim 1, in which: the means for ionciblyopening the secondary valve includes an element connected to the hammerand piston means and extending into the passage means for engagementwith the secondary valve.

6. The invention defined in claim 1, including: resilient means actingon the main valve for absorbing the momentum of the opening main valveand for urging the valve back to the valve-holding means.

7. The invention defined in claim 1, in which: the released pressurefrom the valve chamber is directed to the power chamber for discharge asthe power chamber discharges.

8. The invention defined in claim 7, in which: the rate of discharge ofthe power chamber is adjustable.

9. The invention defined in claim 1, in which: the biased return of thehammer and piston means includes a connection to a source of elasticfluid under pressure.

10. The invention defined in claim 1, in which: the biased return of thehammer and piston means includes a fluid connection to the inlet chamberof such capacity as to carry insuflicient pressure in opposition tomovement of the hammer and piston means in said one direction when theport is open while carrying suflicient pressure to return the hammer andpiston means when the port is closed.

11. The invention defined in claim 1, inwhich: the valve-holding meansinclude magnetic means attracting the main valve to closed position.

12. Vibrator apparatus, comprising: means including a pressurechargeable and dischargeable power chamber having a hammer and pistonmeans movable in one direction upon charging of said chamber and in theopposite direction upon discharge of said chamber; means including aninlet chamber connectible to a source of elastic fluid under pressure;means including a chamber-connect ing port and a main valve for openingand closing the port;

valve-holding means r-eleasably holding the valve closed; meansincluding pressure-chargeable valve chamber and a first pressure areaacting on the valve and exposed to said valve chamber for returning saidmain valve to said valve-holding means when said valve chamber ischarged; means including a second pressure area acting on the valveexposed to inlet chamber pressure and effective upon a predeterminedpressure differential between said areas in favor of said second area toovercome the holding means for opening said valve; and means forregulating the occurrence of said pressure differential, including apassage leading at one end to the valve chamber and at its other end tothe inlet chamber and alternately to a pressure lower than inlet chamberpressure, passage control means operative to allow fluid pressure flowfrom the inlet to the valve chambers upon opening of the valve, to closesaid passage following opening of the valve so as to trap fluid pressurein the valve chamber and thereby to prevent immediate re-opening of thevalve following closing thereof, and said passage control means beingfurther operative to open said valve chamber to a lower pressure uponreturn of the hammer to a predetermined position on its return movementwhereby to release fluid pressure trapped in said valve chamber.

13. The invention defined in claim 12, wherein said passage controlmeans includes an element positively engageable with the hammer uponreturn movement thereof to eflect connection of the valve chamber tosaid lower pressure.

14. The invention defined in claim 12, in which: the valve-holding meansincludes magnetic means releasably holding the valve closed andsupplementing the valve-return action of said first pressure area.

15. The invention defined in claim 12, in which: a seal is provided byan O-ring between the valve and the valve support.

16. The invention defined in claim 12, in which: spring .means isprovided to act on the valve for storing at least part of thevalve-opening momentum releasable as a valveclosing reaction.

References Cited by the Examiner FOREIGN PATENTS 145,126 6/1920 GreatBritain.

SAMUEL LEVINE, Primary Examiner.

1. VIBRATOR APPARATUS, COMPRISING: MEANS INCLUDING A PRESSURE-CHARGEABLEAND DISCHARGEABLE POWER CHAMBER HAVING A HAMMER AND PISTON MEANS MOVABLEIN ONE DIRECTION UPON CHARGING OF SAID CHAMBER AND BIASED FOR RETURNMOVEMENT UPON DISCHARGE OF SAID CHAMBER; MEANS INCLUDING AN INLETCHAMBER CONNECTIBLE TO SOURCE OF ELASTIC FLUID UNDER PRESSURE; MEANSINCLUDING A CHAMBER-CONNECTING PORT, A MAIN VALVE FOR OPENING ANDCLOSING THE PORT, AND A VALVE SUPPORT MOVABLY CARRYING SAID VALVE;VALVEHOLDING MEANS RELEASABLY HOLDING THE VALVE CLOSED; MEANS INCLUDINGA PRESSURE-CHARGEABLE AND DISCHARGEABLE VALVE CHAMBER OPERATIVELYRELATED TO A FIRST PRESSURE AREA EXPOSED TO SAID VALVE CHAMBER FORACTING IN A CLOSING DIRECTION ON SAID MAIN VALVE WHEN SAID VALVE CHAMBERIS CHARGED; MEANS INCLUDING A SECOND PRESSURE AREA ACTING ON THE MAINVALVE AND EXPOSED TO INLET CHAMBER PRESSURE AND EFFECTIVE UPON APREDETERMINED PRESSURE DIFFERENTIAL BETWEEN THE VALVE CHAMBER AND INLETCHAMBER IN FAVOR OF SAID SECOND AREA TO OVERCOME THE HOLDING MEANS FOROPENING SAID MAIN VALVE; AND MEANS FOR REGULATING THE OCCURRENCE OF SAIDPRESSURE DIFFERENTIAL INCLUDING A PASSAGE LEADING AT ONE END OF THEVALVE CHAMBER AND ALTERNATELY CONNECTIBLE AT ITS OTHER END TO INLETCHAMBER PRESSURE WHEN THE MAIN VALVE IS OPEN AND TO A LOWER PRESSUREWHEN SAID MAIN VALVE IS CLOSED SO AS TO RESPECTIVELY CHARGE ANDDISCHARGE SAID VALVE CHAMBER, A SCOENDARY VALVE IN THE PASSAGE YIELDABLETO OPEN TO INLET CHAMBER PRESSURE WHEN THE MAIN VALVE OPENS, WHEREBY TOCHARGE SAID VALVE CHAMBER WITH INLET CHAMBER PRESSURE SO AS TO CAUSERECLOSING OF THE MAIN VALVE, SAID SECONDARY VALVE BEING ARRANGED TOCLOSE SAID PASSAGE INCIDENT TO CHARGING SAID VALVE CHAMBER SO AS TO TRAPPRESSURE IN SAID VALVE CHAMBER AT A VALUE SUFFICIENT TO PREVENT IN SAIDVALVE CHAMBER ON SAID SECOND MAIN-VALVE AREA FROM IMMEDIATELY RE-OPENINGSAID MAIN VALVE, AND MEANS OPERATIVE BY THE HAMMER AND PISTON MEANS UPONPREDETERMINED RETURN MOVEMENT THEREOF TO FORCIBLY OPEN SAID SECONDARYVALVE TO RELEASE SAID TRAPPED PRESSURE FOR DISCHARGING THE VALVE CHAMBERAND THEREBY TO INCUR SAID PREDETERMINED PRESSURE DIFFERENTIAL IN FAVOROF SAID SECOND AREA.